An extrusion-based additive manufacturing system is described in WO2012/037329. The system uses a coated fibre as consumable feedstock. The coated fibre has a core portion and a shell portion with different peak crystallization temperatures. Both the core and the shell portions are melted in an extrusion head, and after they have been deposited the portion with the higher crystallization temperature crystallizes before the other portion. This allows the extruded material to resist gravity and the pressure of subsequent layers, while also reducing distortions.